1. Field of the Invention
The present invention concerns a process for preparing 1,2,3,4-butanetetracarboxylic acid with acceptably low levels of color-forming materials, by steps involving purification of a tetraalkyl butanetetracarboxylate precursor material and hydrolysis of the precursor, and oxidative treatment for purification of the resulting butanetetracarboxylic acid.
The compound 1,2,3,4-butanetetracarboxylic acid has been found by the U.S. Department of Agriculture to be an effective permanent press agent for polyester-cotton blend fabrics, and the compound could find use in large quantities for such purpose. Accordingly, an efficient process for preparing the compound could be very useful. Such a process must produce a product of acceptable color performance properties, as this is an important factor for suitability for permanent press agents. The tetraalkyl butanetetracarboxylates used as reactants in the present process can be prepared from dialkyl maleates by an electrolytic hydrodimerization process as described and claimed in commonly assigned copending application Ser. No. 07/450,773.
2. Description of the Related Art
Procedures have been reported in which 1,2,3,4-butanetetracarboxylic acid is prepared by oxidative cleavage of tetraphthalic acid or anhydride by oxidation with ozone-containing gas, followed by oxygen-containing gas, with the mixture then being heated with a peroxide, e.g. H.sub.2 O.sub.2, at 100.degree. C. to produce the butanetetracarboxylic acid See Japanese patent 55/49336 [80/493363], Apr. 9, 1980, Chem. Abstracts 93 (13) 132082h; and Japanese patent 54/151906 [79/151906], Nov. 29, 1979, Chem. Abstracts 92 (23) 197937 g. Also reported is a procedure in which Delta-4-tetrahydrophthalic anhydride was oxidized with HNO.sub.3, then stirred one hour at 90.degree. C. (oxidative post treatment) to give 1,2,3,4-butanetetracarboxylic acid free of HNO.sub.3, which gave no color on heating 30 minutes at 140.degree. C. in ethylene glycol. Polycarboxylic acids from the HNO.sub.3 oxidation of C.sub.3 -.sub.33 cycloalkenes were purified by an oxidative post treatment; see German Offen. DE 3016225 Al, Oct. 29, 1981, Chem. Abstracts 96 (3) 19672z.
It is known that various organic esters can be converted to free acids by hydrolysis procedures, employing acid, base, or other catalysts, although desirable hydrolysis procedures and conditions may vary considerably with the esters involved. It is also known that in equilibrium reactions, in accord with the law of mass action, the forward reaction rate is generally a function of the concentration of reactants, while the reverse reaction rate is generally a function of the concentration of products. Procedures which give high yields and good production rates are advantageous for commercial production.